Thank you. I learn things EVERY time I watch one of your classes. I re-build vintage audio circuits into guitar amplifiers, and build guitar/audio amplifiers from scratch. Your tutelage is a fundamental cornerstone of my understanding of electronics theory as it applies to what I do. I was worried about you when you weren't feeling so hot, and we hadn't heard from you in a while. I'm sure I speak for a lot of people when I say, I'm very appreciative of you, and I'm very glad you're still sharing your knowledge with us. DC
@AllAmericanFiveRadio
2 жыл бұрын
I've had several questions about covering the full audio spectrum. This simple example of course has a limited spectrum. There are several ways of covering wider frequencies and that would be to target different parts of the spectrum at different stages in amplifier to get a broader coverage. Those of you that are looking for great audio, this method has limitations in harmonics. Let's take a look at a very good negative feedback set up, of course it is much more complex. Please download the PDF so that you can see what I'm talking about. PGF Manual hafler.com/pdf/dynaco/Dyna-ST70.pdf If you take a look at the output tubes, right or left channel, EL - 34, you will see several taps on that audio output transformer. Part of the feedback is the center grid on each push pull. On the bottom center You'll notice the wire continues through a 390 pF to a cathode resistor network on the first half of the 7199, that's another part of the feedback. There's one more and that is the connection The 16 ohm output it also connects through a resister to this cathode resistor network. This feedback network is fantastic I did a video on the frequency response of this amplifier and it is as flat as a pancake. Please watch this video. Dynaco ST 70 Frequency Responce Demo kzitem.info/news/bejne/pHiMrI5mgZthbI4
@ramachandran8666
2 жыл бұрын
Thanks for another well-done video on the NFL and its use in audio circuits
@AllAmericanFiveRadio
2 жыл бұрын
Thank you, and your welcome.
@billharris6886
Жыл бұрын
Hello everyone, KZitem's algorithm just suggested this video, and since I made a career of servicing and designing radios, thought I would add my "2 cents". Thank you Richard for doing all of these helpful videos for those interested in analog electronic circuits normally associated with radio. The intent of my suggestions here is to ensure a greater success rate of a hobbyist building up these circuits and encountering troubles due to component tolerancing plus, at the same time (hopefully) increasing your understanding of the circuit design. This circuit is a two transistor bipolar audio amplifier that will put out enough power to run headphones. This amplifier is operated "Class A", meaning the transistor is biased such that it is conducting throughout the entire 360 degrees of the sinewave or input signal. With Class A, if the amplifier is driven into Cutoff or Saturation, distortion is generated (defeating the purpose). To do this, the Collector (or tube plate, or FET drain) is biased such that it rests at half the power supply voltage (6 Vdc in this case) with no signal is applied. This allows the transistor to have an output swing with a signal that covers the full voltage range available from the circuit. To bias each transistor, select the bias resistors in the voltage divider (the two resistors connected to each Base terminal) to pass about one tenth the collector current (which is about 1 mA in this case). Starting with the first transistor, the collector resistor is 1,000 ohms, and if we want half the power supply voltage dropped across this resistor (6 volts), this results in 6 mA of current. This 6 mA also passes through the collector and emitter of the transistor so, we will have about 0.6 volts dropped across the 100 ohm emitter resistor. The 2N2222 is a Silicon transistor so, will have 0.6 to 0.7 volt drop from Base to Emitter, meaning we will have about 1.2 volts on the Base. Next, compute the voltage divider resistor values to produce 1.2 volts at the base. The closest values will be a 10k for the base to 12 volts and a 1.2k to ground. The second transistor is a bit different in that the resistor to 12 volts is replaced by a transformer. The windings of the transformer will have significantly lower DC resistance than the resistor (probably around 100 ohms) so, the design technique will be somewhat different. To make as few changes to the existing circuit as possible, lets go with the 100 ohm emitter resistor and choose the base bias resistors to give us a collector current of about 12 mA. Using the existing 10k base resistor (going from 12 volts to the base,) change the base to ground resistor to 1.8k, which should provide 1.83 volts at the base and about 1.2 volts on the emitter. This amplifier in its stock form was not distorting the audio, just limiting the frequency response. The two 0.047 uF coupling capacitors are a good choice for a tube or a FET amplifier but, don't work well with bipolar transistors due to the much lower impedance these devices have. Thus, in this case with the 0.047 uF capacitors, the gain of the amplifier will drop off rapidly below 7,500 Hz. To give a typical HiFi frequency response (of 20 Hz to 20,000 Hz), I suggest changing these to 10 uF. If polarized capacitors are used, the positive lead of the first capacitor would need to connect to the base of the first transistor. The second coupling capacitor should have the positive lead connected to the collector of the first transistor. As far as the feedback goes, normally the resistor is in series with the capacitor and the feedback network is connected between the audio input and speaker output. In this case, the feedback was implemented on the last amplifier stage as a simple proof of effectiveness. Hopefully all this makes sense and circuit operation improves.
@AllAmericanFiveRadio
Жыл бұрын
Thank you. You should consider making some videos.
@billharris6886
Жыл бұрын
@@AllAmericanFiveRadio Thanks, I would make videos but, don't have the time.
@radiofun232
2 жыл бұрын
Thanks Richard, a very interesting video where you discuss one of the most important things regarding audio end-amplifiers and pre-amplifiers. Very informative for every electronics hobbyist and professional. 26 may 2022.
@AllAmericanFiveRadio
2 жыл бұрын
Thanks Ko, it's not perfect but it does show what Negative Feedback is and what it does in the circuit.
@activelow9297
Жыл бұрын
Even with your negative feedback, there is a massive rolloff of amplitude below 450hz... and the reason for that is your tiny .047uf coupling capacitors. Change those to .1uf and you will get some nicer low-end response, down to below 100hz.
@AllAmericanFiveRadio
Жыл бұрын
That would help.
@andrewferg8737
2 жыл бұрын
Great video! I'm applying a similar principle to my 5MHz transmitter with a capacitor placed in the base to emitter junction. It decreases the signal slightly, but increases the stability and bandwidth.
@AllAmericanFiveRadio
2 жыл бұрын
Thanks for the information. I'll give this a try.
@andrewferg8737
2 жыл бұрын
@@AllAmericanFiveRadio My output BJT is in the common emitter configuration, so I would suppose that the negative feedback works a bit differently than your common collector output.
@Radio478
Жыл бұрын
Great video thanks
@AllAmericanFiveRadio
Жыл бұрын
Thank you, and your welcome.
@barn5923
2 жыл бұрын
Thanks very much always enjoy them learn a lot
@AllAmericanFiveRadio
2 жыл бұрын
Thank you, and your welcome.
@garygranato9164
2 жыл бұрын
this is brilliant , please expand on this subject/video
@AllAmericanFiveRadio
2 жыл бұрын
I've had several questions about covering the full audio spectrum. This simple example of course has a limited spectrum. There are several ways of covering wider frequencies and that would be to target different parts of the spectrum at different stages in amplifier to get a broader coverage. Those of you that are looking for great audio, this method has limitations in harmonics. Let's take a look at a very good negative feedback set up, of course it is much more complex. Please download the PDF so that you can see what I'm talking about. PGF Manual hafler.com/pdf/dynaco/Dyna-ST70.pdf If you take a look at the output tubes, right or left channel, EL - 34, you will see several taps on that audio output transformer. Part of the feedback is the center grid on each push pull. On the bottom center You'll notice the wire continues through a 390 pF to a cathode resistor network on the first half of the 7199, that's another part of the feedback. There's one more and that is the connection The 16 ohm output it also connects through a resister to this cathode resistor network. This feedback network is fantastic I did a video on the frequency response of this amplifier and it is as flat as a pancake. Please watch this video. Dynaco ST 70 Frequency Responce Demo kzitem.info/news/bejne/pHiMrI5mgZthbI4
@garygranato9164
2 жыл бұрын
@@AllAmericanFiveRadio i've been wondering about a transistor amp with an output transformer for a while now. will it sound better !!
@Bianchi77
2 жыл бұрын
Nice info, thanks, like it :)
@AllAmericanFiveRadio
2 жыл бұрын
Thank you, and your welcome.
@astorina
Жыл бұрын
Thank you many times for your videos and the time you spend for us ! One genuine question : why the first circuit is not linear , is it due to the capacitors between the stage or unwanted capacitance in the circuit or the transistors themselves ? I also understand for the first time that negative is a term related to the phase inversion of the signals involved ! Is this correct ? Thx from Brussel Antonio Brgds
@AllAmericanFiveRadio
Жыл бұрын
The capacitor is a big influence on frequency response. The transistor also has frequency characteristics. How they are used in circuit also influences frequency response. The term Negative mean lots of things, it depends on how it is used. If your talking about negative feedback, that has to do this phasing. Here is a video on this. Audio Amplifier with Negative Feedback Build Oscilloscope Demo kzitem.info/news/bejne/xopmmq6ZgJGnkoY
@RobbyMatthias
3 ай бұрын
Could you tell us more about the transformers' primary and secondary?I would presume the load-primary would be around 1K ohms'?
@AllAmericanFiveRadio
3 ай бұрын
The primary is 230 Ohms and the secondary is 1.6 Ohms.
@devuaudio6785
2 жыл бұрын
Super
@AllAmericanFiveRadio
2 жыл бұрын
thank you , and your welcome.
@pepsodentpasta
2 жыл бұрын
Hi Rick. Some of audio lover don't like a negative feedback due to missing 2nd harmonic signal. Would you mind to explain the correlation between negative feedback and harmonic signal ? Correct me if i"m wrong.
@AllAmericanFiveRadio
2 жыл бұрын
I've had several questions about covering the full audio spectrum. This simple example of course has a limited spectrum. There are several ways of covering wider frequencies and that would be to target different parts of the spectrum at different stages in amplifier to get a broader coverage. Those of you that are looking for great audio, this method has limitations in harmonics. Let's take a look at a very good negative feedback set up, of course it is much more complex. Please download the PDF so that you can see what I'm talking about. PGF Manual hafler.com/pdf/dynaco/Dyna-ST70.pdf If you take a look at the output tubes, right or left channel, EL - 34, you will see several taps on that audio output transformer. Part of the feedback is the center grid on each push pull. On the bottom center You'll notice the wire continues through a 390 pF to a cathode resistor network on the first half of the 7199, that's another part of the feedback. There's one more and that is the connection The 16 ohm output it also connects through a resister to this cathode resistor network. This feedback network is fantastic I did a video on the frequency response of this amplifier and it is as flat as a pancake. Please watch this video. Dynaco ST 70 Frequency Responce Demo kzitem.info/news/bejne/pHiMrI5mgZthbI4
@pepsodentpasta
2 жыл бұрын
@@AllAmericanFiveRadio thank you for your respond.
@SuburbanDon
Жыл бұрын
Anybody who uses 2N2222's is ok with me. This was interesting to watch. Thanks.
@AllAmericanFiveRadio
Жыл бұрын
Thank you, and your welcome.
@PhilipvanderMatten
2 жыл бұрын
What about the full audio spectrum of 20-20kHz?
@AllAmericanFiveRadio
2 жыл бұрын
I've had several questions about covering the full audio spectrum. This simple example of course has a limited spectrum. There are several ways of covering wider frequencies and that would be to target different parts of the spectrum at different stages in amplifier to get a broader coverage. Those of you that are looking for great audio, this method has limitations in harmonics. Let's take a look at a very good negative feedback set up, of course it is much more complex. Please download the PDF so that you can see what I'm talking about. PGF Manual hafler.com/pdf/dynaco/Dyna-ST70.pdf If you take a look at the output tubes, right or left channel, EL - 34, you will see several taps on that audio output transformer. Part of the feedback is the center grid on each push pull. On the bottom center You'll notice the wire continues through a 390 pF to a cathode resistor network on the first half of the 7199, that's another part of the feedback. There's one more and that is the connection The 16 ohm output it also connects through a resister to this cathode resistor network. This feedback network is fantastic I did a video on the frequency response of this amplifier and it is as flat as a pancake. Please watch this video. Dynaco ST 70 Frequency Responce Demo kzitem.info/news/bejne/pHiMrI5mgZthbI4
@boybravo689
Жыл бұрын
Sir by putting a feedback ckt the gain become high is may understanding is correct sir
@AllAmericanFiveRadio
Жыл бұрын
Negative feedback in this circuit levels out, the output over a range of frequencies.
@MrTechHistory
2 жыл бұрын
But... why is it working? Is it changing the bias?
@AllAmericanFiveRadio
2 жыл бұрын
The bias does not change. The negative feed back subtracts from the input signal. The higher the output the more it subtracts from the input signal. The lower the output the less it subtracts from the input signal.
@MrTechHistory
2 жыл бұрын
@@AllAmericanFiveRadio OK - thank you. One more question... How come it's negative instead of positive? Is it because - the output is out of phase with the input?
@AllAmericanFiveRadio
2 жыл бұрын
@@MrTechHistory You use positive feedback for oscillators.
Пікірлер: 42